PARENT SESSION
Symposium 8: Ecosystem response and recovery: Assessing the 1991 Canada-US Air Quality Agreement
Organized by: RA Haeuber, R Birnbaum, and K Timoffee
Tuesday, August 9, 1:30 PM - 5:00 PM, Meeting Room 517 B, Level 5, Palais des congrès de Montréal

Calcium losses from forested watersheds in eastern North America.

Watmough, Shaun^*,1, Aherne, Julian¹, ¹ Environmental and Resource Science Program, Peterborough, ON, K9J 7B8

ABSTRACT- Calcium (Ca) is an important nutrient for terrestrial and aquatic biota. In recent years, Ca concentrations in acid sensitive (Ca typically < 150eq L ^-1) lakes have declined rapidly, partly in response to declining acid leaching and partly due to soil acidification. The declining Ca concentrations have, to varying degrees, offset much of the benefit expected from declining sulphur emissions, and there is increasing concern that Ca may decline to levels that negatively impact both lake and terrestrial biota. Calcium concentrations in lakes are largely determined by inputs from the terrestrial catchment and understanding the processes controlling catchment export is the key to predicting the future Ca-status of lakes and soils. Current studies indicate that the soils of acid-sensitive lake catchments are still acidifying (losing Ca) and therefore Ca levels in lakes will continue to fall until soils cease to acidify. At steady state, the Ca concentration in lakes can be predicted from the difference between Ca inputs (weathering and deposition) and losses (harvesting). At sites that are intensively harvested, Ca concentrations in lakes may be up to 70% lower than current values. However, lakes are rarely at steady state because several factors, including the level of acid leaching, climate and disturbance due to harvesting vary over time, altering Ca export from catchments and therefore surface water Ca concentrations in the short term (years/decades). Current research efforts are directed toward predicting Ca inputs to lakes at steady state and the development of dynamic models that take into account short-term changes in Ca export due to changes in acid leaching, climate variations or harvesting disturbance. Ultimately, chemical changes in lakes and soils will be linked to biological effects.

Key words: calcium, forest soils, lakes